Land Use Controls on the Spatial Variability of Dissolved Black Carbon in a Subtropical Watershed

Rivers export roughly 250 Pg of dissolved organic carbon (DOC) to coastal oceans. DOC exported from rivers can be a reflection of watershed dynamics, and changes in land use can lead to shifts in the molecular composition and reactivity of riverine DOC. About 10% of DOC exported from rivers is dissolved black carbon (DBC), a collection of polycondensed aromatic compounds derived from the incomplete combustion of biomass and fossil fuels. While DOC and DBC export are generally coupled, the effects of watershed land use on DBC quality are not well understood. In this study, DBC samples were collected throughout the Altamaha River watershed in Georgia, USA. DBC was characterized using the benzenepoly­(carboxylic acid) method and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). DBC had a more polycondensed character in areas of the watershed with less anthropogenic disturbance. Furthermore, FTICR-MS revealed that DBC became enriched with a lower molecular weight, heteroatomic signature in response to higher anthropogenic activity. As global land cover continues to change, this study demonstrates on a localized scale that watershed land use can influence the export and composition of DBC, which may have further implications for global carbon and nutrient cycling

Substrate Use of <i>Pseudovibrio</i> sp. Growing in Ultra-Oligotrophic Seawater

<div><p>Marine planktonic bacteria often live in habitats with extremely low concentrations of dissolved organic matter (DOM). To study the use of trace amounts of DOM by the facultatively oligotrophic <i>Pseudovibrio</i> sp. FO-BEG1, we investigated the composition of artificial and natural seawater before and after growth. We determined the concentrations of dissolved organic carbon (DOC), total dissolved nitrogen (TDN), free and hydrolysable amino acids, and the molecular composition of DOM by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR-MS). The DOC concentration of the artificial seawater we used for cultivation was 4.4 μmol C L^-1, which was eight times lower compared to the natural oligotrophic seawater we used for parallel experiments (36 μmol C L ^-1). During the three-week duration of the experiment, cell numbers increased from 40 cells mL^-1 to 2x10⁴ cells mL ^-1 in artificial and to 3x10⁵ cells mL ^-1 in natural seawater. No nitrogen fixation and minor CO₂ fixation (< 1% of cellular carbon) was observed. Our data show that in both media, amino acids were not the main substrate for growth. Instead, FT-ICR-MS analysis revealed usage of a variety of different dissolved organic molecules, belonging to a wide range of chemical compound groups, also containing nitrogen. The present study shows that marine heterotrophic bacteria are able to proliferate with even lower DOC concentrations than available in natural ultra-oligotrophic seawater, using unexpected organic compounds to fuel their energy, carbon and nitrogen requirements.</p></div

Microfluidic-Based Synthesis of Magnetic Nanoparticles Coupled with Miniaturized NMR for Online Relaxation Studies

Using compact desktop NMR systems for rapid characterization of relaxation properties directly after synthesis can expedite the development of functional magnetic nanoparticles. Therefore, an automated system that combines a miniaturized NMR relaxometer and a flow-based microreactor for online synthesis and characterization of magnetic iron oxide nanoparticles is constructed and tested. NMR relaxation properties are quantified online with a 0.5 T permanent magnet for measurement of transverse (<i>T</i>₂) and longitudinal (<i>T</i>₁) relaxation times. Nanoparticles with a primary particle size of about 25 nm are prepared by coprecipitation in a tape-based microreactor that utilizes 3D hydrodynamic flow focusing to avoid channel clogging. Cluster sizes are expeditiously optimized for maximum transverse relaxivity of 115.5 mM s^–1. The compact process control system is an efficient tool that speeds up synthesis optimization and product characterization of magnetic nanoparticles for nanomedical, theranostic, and NMR-based biosensing applications

Purified artificial seawater (medium 3; AS) and natural seawater (NS): Concentrations of dissolved organic carbon (DOC), total dissolved nitrogen (TDN), dissolved free amino acids (DFAA), dissolved combined amino acids (DCAA) and total hydrolysable dissolved amino acids (THDAA) at the different time points: before bottling: only medium; blank: medium poured into serum bottles before inoculation; t₀: directly after inoculation; t₁: 1 week after inoculation; t₂: 3 weeks after inoculation.

<p>(n.d. = not determined).</p

Cell numbers in the different media after 1 and 3 weeks of incubation (initial cell number after inoculation was calculated to be ca. 40 cells mL^-1).

<p>Parallel uninoculated controls were checked for all different media and no cells were observed. (n.d. = not determined; amm. = ammonium; gluc. = glucose)</p><p>Cell numbers in the different media after 1 and 3 weeks of incubation (initial cell number after inoculation was calculated to be ca. 40 cells mL^-1).</p

Summary of FT-ICR-MS results: Numbers of assigned formulas, significantly (p < 0.05) changing and decreasing peaks (N-containing compounds were subset of the overall decreasing compounds) in artificial and natural seawater.

<p>Summary of FT-ICR-MS results: Numbers of assigned formulas, significantly (p < 0.05) changing and decreasing peaks (N-containing compounds were subset of the overall decreasing compounds) in artificial and natural seawater.</p

FT-ICR mass spectra (negative electrospray ionization) from the time points t₀ of (A) artificial seawater and (B) natural seawater.

<p>Asterisks indicate inorganic trace impurities. Inserts show a zoom into the region of mass 325.0 to 325.2 Da. In the negative mode inorganic contaminations suppressed the ionization of organic substances present in low amounts in the artificial seawater.</p

Exemplary growth curve of <i>Pseudovibrio</i> sp. FO-BEG1 in clean artificial seawater (medium 2, counted in triplicates).

<p>Cell numbers (squares) increased to 6×10⁴ cells mL^-1 after 1 week of incubation.</p

Additional file 7: Table S9. of A comprehensive study of the genomic differentiation between temperate Dent and Flint maize

Gene-wise level of differentiation of allele frequencies between landraces and Dent (left) and Flint (right) elite lines based on genotyping data. (XLSX 27 kb

Additional file 2: Figure S1. of A comprehensive study of the genomic differentiation between temperate Dent and Flint maize

Metrics of the selection screens for 136 temperate inbred lines along the ten maize chromosomes based on genotyping data. (PDF 4242 kb